About Excretion and homeostasis in O Level Biology
Excretion and homeostasis is one of the 13 main topics in our O Level Biology (Cambridge (CAIE) 5090) question bank, and about 6% of its real questions come from it. Tayyari Karo has 35 real questions on this topic from 2021 to 2026, from Paper 1, Paper 2, Paper 4; 28 are multiple choice and marked instantly, and the rest are structured questions with a model answer. By difficulty: 30 medium, 3 easy, 2 hard.
Work through the questions below, then open the explanation for each one. Redo the ones you missed a few days later.
Try 7 real questions
These are real past-paper questions. Think of your answer first, then open the explanation.
May/June 2026 · Paper 1 · Excretion and homeostasis
When the body temperature of a dog is low, muscles attached to body hairs contract and cause the body hairs to stand upright. How does this help to maintain the dog's body temperature?
- The upright body hairs trap air and air provides good insulation.
- The upright body hairs trap air and air provides poor insulation.
- The upright body hairs trap water lost through sweating and water provides good insulation.
- The upright body hairs trap water lost through sweating and water provides poor insulation.
Show answer and explanation
Answer: A. The upright body hairs trap air and air provides good insulation.
Trapped air is a good insulator, so less heat is lost.
May/June 2025 · Paper 1 · Excretion and homeostasis
Which process is not part of a homeostatic mechanism in mammals?
- change in flow of blood in vessels of the skin
- growth of longer hairs from the skin
- increased rate of sweat production
- contraction of hair erector muscles
Show answer and explanation
Answer: B. growth of longer hairs from the skin
Hair growth is a long-term change, not a rapid corrective response to a change in conditions.
Oct/Nov 2025 · Paper 1 · Excretion and homeostasis
An athlete's body temperature rose from 37.0 to 38.6 C after exercise, then fell to 37.2 C after 10 min rest. Which events lower the temperature (arterioles near skin surface / heat lost through)?
- contract / evaporation of sweat
- contract / shivering
- dilate / evaporation of sweat
- dilate / shivering
Show answer and explanation
Answer: C. dilate / evaporation of sweat
Oct/Nov 2024 · Paper 1 · Excretion and homeostasis
When a person is frightened, which substance causes an increase in blood sugar level?
- adrenaline
- carbon dioxide
- insulin
- lactic acid
Show answer and explanation
Answer: A. adrenaline
Oct/Nov 2023 · Paper 1 · Excretion and homeostasis
Some people require dialysis to remove waste products and excess salts from their blood. For these individuals, which part of the body is not functioning correctly?
- bladder
- heart
- kidney
- ureter
Show answer and explanation
Answer: D. ureter
Oct/Nov 2022 · Paper 1 · Excretion and homeostasis
How do the concentrations of oxygen and urea in the renal artery compare to their concentrations in the renal vein? (oxygen in renal artery / urea in renal artery)
- higher / higher
- higher / lower
- lower / higher
- lower / lower
Show answer and explanation
Answer: A. higher / higher
May/June 2021 · Paper 2 · Excretion and homeostasis
Excess amino acids are broken down in liver cells to form urea. (a) Describe the pathway taken by a molecule of urea, from the liver of a mammal until it reaches the soil. (b) Urea contains nitrogen. Suggest why it is important that molecules that contain nitrogen are added to the soil.
Show model answer
(a) Urea enters blood/plasma; travels via hepatic vein to vena cava/heart; to kidney via renal artery; filtered from blood into urine; down ureter to bladder; out via urethra; excreted; reaches soil in urine/faeces as fertiliser. (b) Nitrogen is cycled/replenished; nitrifying/nitrogen-fixing bacteria convert it to nitrates; plants absorb nitrates to make proteins/amino acids; increases soil fertility / crop growth; animals obtain protein from plants.
